Device-independent entanglement-based Bennett 1992 protocol

In this paper we set forth a connection between the Bennett 1992 protocol and a Bell inequality. This allows us to extend the usual prepare-and-measure protocol to its entanglement-based formulation. We exploit a recent result in the framework of device-independent quantum key distribution to provide a simple, model-independent, security proof for the protocol. The minimum efficiency required for a practical implementation of the scheme can be as low as 75% in the completely untrusted case and 50% in case the sender is assumed to be trusted.